We identified Rho kinase ROCK1 as caspase-3 target in human failing hearts. The cleavage resulted in a constitutively active Rho kinase, ROCK?1. We also demonstrated that genetic deletion of ROCK1 inhibited stress-induced cardiac fibrosis. However, the function of ROCK?1 and molecular signaling linking ROCK1 to cardiac fibrosis remain obscure. The goal of the study is to determine the fibrogenic role of ROCK?1 and investigate molecular mechanism of ROCK?1-mediated cardiac fibrosis. To address these questions, we generated transgenic mice expressing ROCK?1 in heart to mimic human heart disease. Overt cardiac fibrosis was observed with marked upregulation of TGF1 in the transgenic mice. Since activation of Rho kinase increased SRF activity, we assessed the transgenic heart and found manifest increase in SRF activity. Our preliminary results suggested SRF as a potential regulator of TGF1. We also found robust increases in NF-?B expression and activity in the mice. Therefore, the central hypothesis is that constitutive activation of ROCK1 in cardiomyocytes is sufficient to result in cardiac fibrosis by upregulating TGF signaling and other pro-fibrotic cytokines through activation of SRF and NF-?B, respectively. Three aims will be completed. Aim I is to determine the pro-fibrotic effect of ROCK?1 in intact heart. The transgenic mice will be studied under basal and stress challenging conditions. The fibrogenic phenotype will be determined in two mouse lines with high and low expression level of ROCK?1. A rescue experiment by Rho kinase inhibitor will be conducted. Aim II is to elucidate the molecular mechanisms of ROCK?1-mediated cardiac fibrosis. The signaling pathway linked between Rho kinase and fibrotic response has been proposed with a considerable amount of preliminary data. The proposed mechanism includes the upregulation of TGF1 and NF-?B-mediated cytokines. The hypothesis will be tested in vitro in cardiomyocytes and in vivo in the transgenic mice. To investigate SRF-directed TGF1 regulation, the identified cis elements in TGF1 promoter/enhancer region will be verified by extensive experiments including 1) luciferase, EMSA and CHIP assay; 2) through transgenic mice expressing lacZ driven by either the wild or mutant cis elements; 3) by analyzing expression of TGF1 in SRF null mouse heart, where the decrease in TGF?1 level is expected. Aim III is to determine if the loss of endogenous ROCK1 inhibitor, Rnd3, recapitulates ROCK?1-mediated fibrotic cardiomyopathy. The fibrotic phenotype, Rho kinase activity, TGF? and NF-?B signaling will be assessed under normal and stress challenging conditions. The outcome of the proposal will be to establish links between the activation of Rho kinase, TGF1 and NF-?B signaling in fibrotic cardiac remodeling. The innovation of the proposal includes 1) demonstration of fibrogenic role of ROCK?1; 2) elucidation of the ROCK1->SRF->TGF?1->fibrosis and the ROCK1->NF-?B->cytokines->fibrosis signaling pathways; 3) revelation the role of Rnd3 in cardiac remodeling; and 4) implication of manipulating Rho kinase activity and caspase cleavage as candidate therapeutic targets.